American Board of Surgery Qualifying Exam (ABS QE) Practice Test

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What is the key regulator in the management of calcium levels in the body?

Epinephrine
Insulin
Calcitonin
Parathyroid hormone

The correct answer is: Parathyroid hormone

The management of calcium levels in the body is predominantly regulated by parathyroid hormone (PTH). PTH is secreted by the parathyroid glands in response to low serum calcium levels. When calcium levels drop, PTH is released into the bloodstream, leading to several physiological effects aimed at increasing calcium concentrations in the blood. PTH acts on the bones, kidneys, and intestines to elevate calcium levels. In the bones, it stimulates the release of calcium by promoting the activity of osteoclasts, which break down bone tissue. In the kidneys, PTH enhances the reabsorption of calcium and decreases the reabsorption of phosphate, facilitating increased calcium levels in the bloodstream. Additionally, PTH promotes the conversion of vitamin D into its active form (calcitriol) in the kidneys, which in turn increases intestinal absorption of calcium. Thus, parathyroid hormone is crucial in maintaining calcium homeostasis and is the primary regulator in response to changes in serum calcium concentrations. This role is distinguished from other hormones listed, such as calcitonin, which helps reduce calcium levels when they are excessively elevated, but is not the key regulator like PTH.